The invention relates to the art of electric arc welding and more particularly to an electric arc welder having a controlled voltage or current output with the variable or universal AC input that ranges up to about 600 VAC.
The invention relates to a unique electric arc welder having a dual intermediate stage operated by a power factor control chip whereby a unique architecture allows the input to vary drastically up to 600 volts while the controlled output weld current and/or weld voltage is controlled in the DC welding range. By utilizing the unique architecture of the power factor control dual intermediate stage in combination with an output converter, the power supply for the electric arc welder can have high input voltage variable in magnitude with an output power exceeding two to three kilowatts. Since there are several topographies relating to this type of power supply for use in low rated appliances, several items of prior art are incorporated by reference herein as background information for evaluating uniqueness and superiority of the present invention. The invention relates to power factor correcting power supplies capable of producing a high power rating needed for welding. This feature requires consideration of welding prior art also.
For some time, it has been known to use a boost type power factor correction with an electronic switch controlled by a power factor correcting circuit in the form of a chip. An early version of this architecture is shown in Wilkinson U.S. Pat. No. 4,677,366 which is incorporated by reference for background information. This early power supply does not use the novel architecture of the present invention and can be used for only low power applications.
In Donner U.S. Pat. No. 5,149,933 a boost converter uses a high speed operated switch that can be operated by a power factor controller circuit No. ML 4812 made by Micro-Linear Corporation. This circuit provides a current to a charging capacitor bank throughout the full 180xc2x0 of each half cycle of the fill wave rectified line voltage. The power factor control chip uses a transformer to apply output energy to the weld operation. This patent appears to be an early laboratory type single phase power supply with a power factor correcting circuit allegedly capable of welding. Current and voltage feedback 1 allegedly controls the pulse generator that operates the switch when there is no power factor control feature used in this early laboratory power supply. This patent discloses background information of an early attempt to use power factor control in a welding installation. Donner U.S. Pat. No. 5,149,933 is incorporated by reference herein as background information only. There is no dual stage inverter, nor output converter.
Since the present invention relates to an architecture wherein a boost converter, albeit a dual stage, drives a DC to DC output converter, Vinciarelli U.S. Pat. No. 5,786,992 is relevant because it shows a related low voltage circuit of this type used for lighting installations. The power factor control is discontinuous whereby input current does not flow at all times. The output power is very limited and the input voltage is fixed at commercial line voltage. This patent does not relates to welding or any other high power technology. However, the patent is incorporated by reference herein merely to show a boost converter for driving a transformer that powers a DC to DC converter using a standard power factor correcting circuit. Such low voltage power factor control circuit for fixed AC input with input voltage less than 220 volts and power ratings less than about 50 watts are somewhat standard at least in the patented technology, but not in practice. Another low power boost circuit with power factor control capabilities is shown in Shikata U.S. Pat. No. 5,917,711 also incorporated by reference. This patent illustrates a boost converter for power factor correction with an output circuit driven by a transformer. The power factor circuit utilizes the input current wave form. This prior low rated power supply can not be used for welding. Turning now to welding power supplies, a power supply circuit having a power factor correcting feature with an output transformer to drive a welding circuit is shown in Moriguchi U.S. Pat. No. 5,864,110. This power supply is used for arc welding; however, it does not have an output stage which allows utilization of a standard DC link that is converted to the necessary welding current and voltage. This patent is incorporated by reference herein.
The Lincoln Electric Company has issued United States patent relating to the use of power factor correcting circuits in various architecture used for electric arc welding. These patents are Kooken U.S. Pat. No. 5,991,169, Church U.S. Pat. No. 6,023,037 and Blankenship U.S. Pat. No. 6,091,612. Each of these power supplies includes power factor correcting feature; however, they do not use the unique architecture for delivery of AC voltage that is converted to a DC link to be converted to low voltage DC use in arc welding. The patents by Lincoln Electric are incorporated by reference herein as background information in that they relate to welding power supplies, but not the architecture of the present invention.
The low power supply circuits constituting the above background information can not be used for welding. Further, those patents incorporated by reference herein that disclose prior attempts to resolve problems associated with electric arc welding use architecture quite different than used in practicing the present invention. All of this background information discloses a body of technology need not be repeated. The specific architecture of the present invention and the novelty thereof is set forth in this disclosure build on or replaces such prior efforts.
The invention utilizes a dual stage boost inverter circuit with power factor correcting capabilities similar to the circuit shown in an article by Wei Batarseh, and Zhu in an article entitled A Single-Switch AC/DC converter with Power Factor Correction, dated May 2000. This IEEE article is incorporated by reference herein as background information to explain the operation of the inverter concept for creating the AC output with a controlled power factor for the input. This laboratory type power supply can not be used for welding. The input is less than 220 volts and the power rating is considerably less than 50 watts. This article is incorporated by reference herein as background information.
As indicated by the several prior art patents constituting background, a substantial amount of effort was devoted in the 1980""s to develop a power supply for high volume domestic industrial appliances that could be connected to a single phase line voltage and maintain a high power factor or low harmonic distortion. This extensive research and development endeavor was intensified by the need to increase the efficiency and thus reduce the electrical power consumed in large volume by small domestic appliances throughout the nation. These power supplies were designed to use a boost converter, buck converter or flyback converter with specially designed power factor correcting chips using controlled switching of the converter to assure high input power factors and low harmonic distortion. These small power supplies normally created less than 2000 watts of power and were not usable for industrial applications. In the mid 1990""s, the electric arc welding industry was using inverter type power supplies with high switching frequency; however, power factor correcting technology for such power supplies did not exist. Consequently, electric arc welders presented a problem with power consumption. There were no techniques to control the power factor of the input lines driving electric arc welders. This was even more pronounced with input that could be as high as 600 VAC.
In the mid 1990""s, a few of the companies in the electric arc welding field started experimenting with modifying power factor control power supplies to create a high capacity power supply for welding and plasma cutting. Then, it was realized that merely converting existing power supplies to welding power supplies was not the proper development direction. Thus, The Lincoln Electric Company of Cleveland, Ohio took a different tack. Power supplies were tailored for welding. At first such efforts involved only an attempt to use low power units for high power welding. This was not commercially successful. This effort has resulted in several patents by The Lincoln Electric Company, such as Kooken U.S. Pat. No. 5,991,169, Church U.S. Pat. No. 6,023,037 and Blankenship U.S. Pat. No. 6,091,612 all of which disclose special power supplies with the inverter stages with a power factor correcting feature having the ability to create a high output power for electric arc welding. These patents disclose switching power supplies with specific inverter topographies with output chopper stages in most instances. All of these prior efforts to provide electric arc welders with specially developed power supplies having power factor correcting capabilities presented certain functional limitations. Consequently, it was desirable to develop a new architecture which could be driven by high voltage input power up to approximately 600 VAC while having a controlled output of welding voltage in the range of 20-100 VDC. To combine these two completely different, diverse electrical voltage concepts, there was a need to develop a specific architecture for accomplishing this objective while still maintaining high power factor and low harmonic distortion.
The requirements of electric arc welding capable of converting single or three phase high voltage electrical input to a low voltage DC, with high output power for electric arc welding is accomplished by the present invention. A dual stage boost converter with a power factor correcting circuit controlled by a high speed switch provides a driven inverter network that converts rectified input voltage to an AC output in a manner still maintaining high power factor. By using a driven inverter stage at the output of the power factor correcting boost converter, a specific voltage across an output transformer can produce a low voltage output DC link of approximately 100 VDC. A driven inverter avoids the pitfalls of a resonant inverter. The controlled DC link is then converted by a DCxe2x80x94DC converter in the form of a down chopper to produce the necessary DC voltage for electric arc welding. By using current and voltage feedback the current and voltage for the welding operation is controlled. Of course, a wave shape circuit could be used at the output converter for controlling the wave shape of the current being used for the electric arc welding output.
In accordance with the invention, there is provided an electric arc welder with a variable DC voltage input of up to 600 VAC and a rectifier to provide a DC link with a first and second lead. A driven high frequency boost stage with an inverter output to an isolation transformer gives an AC voltage that is rectified to produce the first DC link. The boost converter has an inverter stage that is operated at a high frequency but still allows high power transfer. The boost stage converter comprises an inductor, a first series output branch with the first primary winding connected to the first lead and a first capacitor connected to the second lead, a second series output branch with a second primary winding connected to the second lead and a second capacitor connected to the first lead and a high frequency operated switch. The switch is connected between the leads and has an open condition charging the capacitor through the primary windings with current flow in a first direction and discharging the inductor and a second condition charging the inductor through the primary winding with current flow in a second direction and discharging the inductor to charge the capacitors. The switch is operated by a power factor control circuit at a frequency greater than about 18 kHz. This boost stage or converter has an AC output comprising the secondary winding network of an isolation transformer powered by the current flow in the first and second primary windings. A rectifier converts the AC output from the transformer to a first DC voltage and a DC/DC converter converts the first DC voltage to a second DC voltage connected across the arc of a welding station. The arc has a controlled weld current or voltage. By this architecture, the input can vary while maintaining a fixed weld voltage.
In accordance with another aspect of the invention, there is a diode poled in the direction from the first lead to the second lead and connected in series between the first and second capacitors to clamp the capacitors as they are charged to a controlled voltage. The switch for charging and discharging the capacitors has a rating of 30-75 amperes which is substantially greater than the low capacity current switches used in the standard power factor connecting power supplies. The first DC voltage is in the control range of 75-113 VDC. Thus, the magnitude and frequency of the arc not input voltage is determining parameters of the output voltage. The first DC link voltage is less than 113 VDC and preferably about 100 VDC. The weld voltage is 20-100 VDC.
In accordance with another aspect of the present invention, the output of the power supply is a buck converter with a switch operated by a pulse width modulator. The pulse width modulator is controlled by a weld current feedback voltage, a weld voltage feedback voltage or combinations thereof. The switch is operated at a frequency in excess of 18 kHz.
The primary object of the present invention is the provision of a high speed switching power supply having power factor correcting capabilities and capable of use in electric arc welding.
Another object of the present invention is the provision of an electric arc welder using the power supply as defined above.
Still a further object of the present invention is the provision of an electric arc welder that has high voltage input capabilities and uses a driven boost and inverter stage.
Another object of the present invention is the provision of a high speed switching circuit power supply for electric arc welding having a power factor correcting circuit and capable of universal input voltage with a controllable weld voltage.
These and other objects and advantages will become apparent from the following description taken together with the accompanying drawings.